I wanna recommend you guys fans by the German Company called Blacknoise.
These are the most quiet fans on the market and perfect for all off your needs.
I built a lot of computers since I am a professionell custom computer builder from Germany so I put them in a ton of computers out there.
If a computer has to be absolutely silent I always use them... You won't find anything better then them!
You can easily use 15+ of them and you will not hear anything!